1. Field of the Invention
This invention relates to a method for the transmission of information by HF or VHF type radio over relatively long distances that exclude any possibility of direct radio link-up and in regions not covered by air-to-ground relay systems. This does not of course exclude the utilisation of this system over shorter distances and even in zones equipped with other relay systems.
It applies notably to air-to-ground communications for data links D/L in the field of medium or long-range air transport.
2. Description of the Prior Art
In a general manner, it is known that, for this type of application, the main means of communication currently used are:
telecommunications satellite networks (SATCOM D/L), PA0 radio transmission (VHF D/L, HF D/L), PA0 radar systems (S mode D/L).
Experience has proved that these different solutions have a certain number of drawbacks.
In fact, the major drawback of VHF type radio communication systems is that their range is limited to radio horizon (radioelectric range by direct propagation). This drawback can only be obviated by the installation of relays between two stations situated out of radio range.
S mode D/L has a similar drawback related to radar range.
It thus appears that, in air transport, only satellite communications (SATCOM), when available, are applicable when flying over ocean or desert regions.
Nevertheless, this solution is still expensive when complete global coverage is required, as presently existing systems require that a large number of satellites be maintained in service in order for one or two satellites to be in view at every point on the globe.
Moreover, this solution puts the user in a position of total dependence with regard to the satellite network owner.